linux-kernel - Re: [PATCH] x86/MCE/AMD: Allow thresholding interface updates after init

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Date:   Wed, 29 Dec 2021 18:42:18 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yazen Ghannam <yazen.ghannam@....com>
Cc:     linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        tony.luck@...el.com, x86@...nel.org,
        Smita.KoralahalliChannabasappa@....com
Subject: Re: [PATCH] x86/MCE/AMD: Allow thresholding interface updates after
 init

On Tue, Dec 07, 2021 at 07:30:28PM +0000, Yazen Ghannam wrote:
> Changes to the AMD Thresholding sysfs code prevents sysfs writes from
> updating the underlying registers once CPU init is completed, i.e.
> "threshold_banks" is set.
> 
> Allow the registers to be updated if the thresholding interface is
> already initialized or if in the init path. Use the "set_lvt_off" value
> to indicate if running in the init path, since this value is only set
> during init.
> 
> Fixes: a037f3ca0ea0 ("x86/mce/amd: Make threshold bank setting hotplug robust")
> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>

We want that in stable, right?

> ---
>  arch/x86/kernel/cpu/mce/amd.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
> index 2eadc7c4c902..408c9546ea0b 100644
> --- a/arch/x86/kernel/cpu/mce/amd.c
> +++ b/arch/x86/kernel/cpu/mce/amd.c
> @@ -400,8 +400,12 @@ static void threshold_restart_bank(void *_tr)
>  	struct thresh_restart *tr = _tr;
>  	u32 hi, lo;
>  
> -	/* sysfs write might race against an offline operation */
> -	if (this_cpu_read(threshold_banks))
> +	/*
> +	 * sysfs write might race against an offline operation.
> +	 * Prevent register writes if threshold_banks are not set and this is
> +	 * not called from the init path as indicated by "set_lvt_off".
> +	 */

So if you convert this text into code, it would read like:

	if (!this_cpu_read(threshold_banks) && !tr->set_lvt_off)

which is equivalent to:

> +	if (!(this_cpu_read(threshold_banks) || tr->set_lvt_off))

but easier to follow, methinks.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette